Tunneling-Magnetoresistance Vector Magnetometer with Deflection Flux-Chopper

We report the prototype of a vector magnetometer comprising in-plane tunneling-magnetoresistance (TMR) sensors and a flux chopper. The flux chopper deflects the magnetic flux at 1 kHz, thereby enabling the out-of-plane sensing capability while reducing the low-frequency noise for the TMR sensors. The observed out-of-plane and in-plane sensitivities are 98 and 125 V/T, respectively. Due to experimental tolerances and environmental effects, certain errors are unavoidable, e.g., misalignment of the sensors and the chopper, offset, gain errors, and influence of the power supply. Thus, a linear correction process was performed to eliminate all these errors using the voltage-to-field matrix. The evaluated results of the device as an electronic compass showed that the three-axis outputs were linear and orthogonal to each other, and the maximum angle error was found to be less than ±1°. In addition, the field noise at 1 Hz was found to be 0.2 nT/Hz with deflection flux chopping. The results indicate that deflection flux chopping is a promising method to implement a low-noise vector magnetometer with coplanar TMR sensors.